Sealed honeycomb structure and method of producing the same

ABSTRACT

There is disclosed a plugged honeycomb structure  1  having: partition walls  2  arranged in such a manner as to form a plurality of cells  3  extending from one end face  42  to the other end face  44  through an axial direction; an outer peripheral wall  7  which surrounds an outer periphery of the partition wall  2 ; and plugging portions  4   a,    4   b  disposed in such a manner as to plug the cell  3  in either end face  42, 44 . In the plugged honeycomb structure  1 , at least some of plugging portions  4   a  arranged in at least the vicinity of the outer peripheral wall protrude from the end face  42  or  44 . Alternatively, there are provided a plugged honeycomb structure  1  in which a tip of the protruding portion  4   a  is substantially flat or has a moderate curved face, and a method of manufacturing the structure. The plugged honeycomb structure  1  does not easily break, is capable of enhancing durability, and is preferably usable in a filter such as a diesel particulate filter (DPF).

TECHNICAL FIELD

The present invention relates to a plugged honeycomb structure and amethod of manufacturing the structure, particularly to a honeycombstructure having plugging portions, which does not easily break andwhich is capable of enhancing durability and which is preferably usablein a filter such as a diesel particulate filter (DPF), and a method ofmanufacturing the structure.

BACKGROUND ART

When a honeycomb structure is used as a filter such as a DPF, ingeneral, as shown in FIGS. 11(a) to (c), the structure is used in theform of a plugged honeycomb structure 1 having: porous partition walls 2arranged in such a manner as to form a plurality of cells 3 eachextending from one end face 42 to the other end face 44 in an axialdirection; an outer peripheral wall 7 which surrounds outer peripheriesof the partition walls 2; and plugging portions 4 which are arranged insuch a manner as to plug the cells 3 in either end face. By thisconfiguration, a fluid to be treated flows into the cell from one endface 42, and is discharged from the other end face 44 via another cell 3through the porous partition wall 2. In this case, the partition wall 2constitutes a filter to capture particulate matters.

Moreover, as shown in FIG. 12, the plugged honeycomb structure is storedin a can member 20 formed of a metal in a state in which a mat 24 formedof a ceramic is wound around an outer peripheral wall of the structure.The structure is fixed by an annular fixing member 22 disposed in thecan member and formed of a metal, attached to an automobile or the like,and used in some case (see, e.g., Japanese Patent Application Laid-OpenNo. 8-281034).

The plugged honeycomb structure for use in this application hasrequirements that the structure does not easily break by vibration,pressure loss is small, and resistance to thermal shock is satisfactory.

In a case where the plugged honeycomb structure is used for the DPF, aplugged honeycomb structure has been proposed in which a protrudingportion is formed on plugging portions, protruding in a tapered shapetoward an upstream side from the end face of the cell, as a method ofpreventing rapid increase of the pressure loss by deposition of theparticulate matters (see, e.g., Japanese Patent Application Laid-OpenNo. 2002-309922).

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a plugged honeycombstructure in which a pressure loss is reduced from a viewpoint differentfrom that of the above-described proposal and whose breakage does noteasily occur, and a method of manufacturing the structure.

The present inventor has studied cracks that can be generated in thevicinity of an outer peripheral wall in detail in order to solve theproblem. As to a conventional plugging portion, as shown in FIG. 11(c),a tip is formed substantially on the same face as an end face 42.Therefore, as shown in FIG. 12, in a case where the plugged honeycombstructure is fixed in a can member 20 by an annular fixing member 22fixed to the can member 20, an end portion of a partition wall isbrought into direct contact with an end portion of the outer peripheralwall and the fixing member 22. Moreover, when a fluid to be treatedflows into the can member 20, such as an exhaust gas at hightemperature, the can member 20 and the fixing member 22 are heated andexpanded. Accordingly, the fixing member 22 moves toward an outerperiphery while pressing the end face 42. Therefore, in a case wherelarge heat is applied, it is supposed that cracks are generated in theend face in the vicinity of the outer peripheral wall by a stressreceived during this movement. A metal wire is knitted into a net shapeto form a wire mesh ring (not shown) into a ring shape, and the ring issometimes disposed as a cushion material between the fixing member 22and the end face 42. In this case, the wire mesh ring is brought intodirect contact with the end face 42, and further bites in an opening ofa cell which is not plugged. Moreover, it is also supposed that when thefixing member moves, the wire mesh moves, and a stress is applied to thepartition wall of a portion bitten by the wire mesh to induce cracks.

Moreover, when the opening of the cell in the vicinity of the outerperipheral wall is covered with the fixing member 22, the fluid to betreated does not flow into the cell in the vicinity of the outerperipheral wall, the cell cannot perform a function of a filter, andpressure loss increases. When the fluid to be treated at hightemperature does not flow into the cell in the vicinity of the outerperipheral wall, a temperature difference is made from an inner cellinto which the fluid to be treated at the high temperature flows, and itis supposed that cracks are easily generated by thermal shock.

In the present invention, based on this finding, a contact state of thefixing member with respect to the vicinity of the outer peripheral wallis improved, accordingly a possibility is reduced that the cracks aregenerated in the vicinity of the outer peripheral wall, and the pressureloss is reduced. That is, there is provided a plugged honeycombstructure having: partition walls arranged in such a manner as to form aplurality of cells extending from one end face to the other end facethrough an axial direction; an outer peripheral wall which surrounds anouter periphery of the partition wall; and plugging portions disposed insuch a manner as to plug the cell in either end face, characterized inthat at least some of the plugging portions arranged in at least thevicinity of the outer peripheral wall protrude from the end face, and atip of a protruding portion is substantially flat or has a moderatecurved face.

In the plugged honeycomb structure of the present invention, furthersome or all of the plugging portions arranged in a portion other thanthe vicinity of the outer periphery protrude from the end face, and thetip of the protruding portion is preferably substantially flat or hasthe moderate curved face. The structure preferably has a pluggingportion including a protruding portion including a portion whosesectional shape crossing the axial direction at right angles issubstantially circular. The structure also preferably has a pluggingportion including a protruding portion including a portion whosesectional shape crossing the axial direction at right angles is asubstantially polygonal shape, and the substantially polygonal shapefurther preferably has a shape whose corner portion has been cut into alinear or curved shape. The structure preferably has a plugging portionincluding a protruding portion whose sectional shape parallel to theaxial direction is a substantially quadrangular shape, and thesubstantially quadrangular shape is further preferably a shape whosecorner portion has been cut into a linear or curved shape. In theplugged honeycomb structure of the present invention, a maximum heightfrom the end face to the tip of each protruding portion is preferablysubstantially equal. Porosity of the protruding portion is preferablysmaller than that of another portion of the plugged honeycomb structure.

Moreover, according to the present invention, there is provided a methodof manufacturing a plugged honeycomb structure comprising: preparing ahoneycomb structure comprising porous partition walls arranged in such amanner as to form a plurality of cells extending from one end face tothe other end face through an axial direction, and a plugging step ofplugging at least some of the cells in either end face, characterized inthat the plugging step includes: a masking sub-step of disposing a filmon the end face in such a manner as to mask some of the cells; and afilling sub-step of filling a predetermined cell which is not maskedwith a plugging material, and the filling sub-step includes: filling thecell with the plugging material up to a height which is not less than aheight equal to that of an upper face of the film.

In the filling sub-step of the present invention, the plugging materialis preferably applied at least twice. Further in the filling sub-step,the plugging material is also preferably applied once. Furthermore, theplugging material is a slurry including a liquid, and the liquid ispreferably a liquid which does not substantially penetrate into thepartition wall. In the masking sub-step of the present invention, thefilm is disposed in such a manner as to cover all the cells, a hole ispreferably made in a portion of the film, corresponding to apredetermined cell, and a hole is further preferably made in such amanner that periphery of the hole is raised in a thickness direction ofthe film. Moreover, the plugging material is a slurry containing aliquid, and viscosity of the slurry is 10 to 1000 dPa·s, furtherpreferably 100 to 600 dPa/s. The plugging material is also preferably aslurry containing at least one type selected from a group consisting ofa powdered organic material derived from plant, powdered syntheticresin, powdered carbon-based material, hollow synthetic resin, solidnormal-temperature liquid or gas material, high-melting material, porousmaterial, and hollow inorganic material. After filling the cell with theplugging material, volume of the plugging material is expanded, and theprotruding portion is preferably protruded from the filter end face.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a perspective view schematically showing one example of aplugged honeycomb structure of the present invention, and FIG. 1(b) is aparallel sectional view;

FIG. 2(a) is a partially enlarged parallel sectional view schematicallyshowing one example of plugging portions according to the presentinvention, FIG. 2(b) is a partially enlarged parallel sectional viewschematically showing another example of plugging portions according tothe present invention, and FIGS. 2(c) to (h) are partially enlargedparallel sectional views schematically showing still another example ofplugging portions according to the present invention;

FIGS. 3(a) to (e) are partially enlarged parallel sectional viewsschematically showing still another example of plugging portionsaccording to the present invention;

FIG. 4 is a partially enlarged parallel sectional view schematicallyshowing a relation between the plugged honeycomb structure and a fixingmember in the present invention;

FIGS. 5(a) and (b) are partially enlarged parallel sectional viewsschematically showing still another example of plugging portionsaccording to the present invention;

FIGS. 6(a) and (b) are orthogonal section partially enlarged viewsschematically showing still another example of plugging portionsaccording to the present invention;

FIG. 7(a) is a perspective view schematically showing one example of ahoneycomb structure for use in a manufacturing method of the presentinvention, and FIG. 7(b) is a partially enlarged plan view;

FIG. 8 is a partially enlarged parallel sectional view schematicallyshowing a masking sub-step in the manufacturing method of the presentinvention;

FIG. 9(a) is a partially enlarged parallel sectional view schematicallyshowing one preferable example of the masking sub-step in the presentinvention, and FIG. 9(b) is a partially enlarged parallel sectional viewschematically showing one preferable example of a filling sub-step;

FIG. 10 is a partially enlarged parallel sectional view schematicallyshowing one preferable example of the filling sub-step in the presentinvention;

FIG. 11(a) is a schematic perspective view showing one example of aconventional plugged honeycomb filter, and FIG. 11(b) is a partiallyenlarged plan view, and FIG. 11(c) is a partially enlarged parallelsectional view;

FIG. 12 is a schematic parallel sectional view showing a state in whichthe conventional honeycomb filter is stored in a can;

FIG. 13 is a partially enlarged parallel sectional view schematicallyshowing one example of a conventional plugging portion; and

FIG. 14(a) is a parallel sectional view schematically showing aconventional filling sub-step, and FIG. 14(b) is a partially enlargedparallel sectional view.

BEST MODE FOR CARRYING OUT THE INVENTION

A plugged honeycomb structure and a method of manufacturing thestructure according to the present invention will be describedhereinafter in detail based on a specific embodiment. The presentinvention is not limited to the following embodiment. It is to be notedthat a section crossing an axial direction (for example, an axialdirection shown in FIG. 1) at right angles will be hereinafter referredto as an orthogonal section, and a section parallel to the axialdirection will be referred to as a parallel section.

As shown in FIGS. 1(a), (b), a plugged honeycomb structure 1 of thepresent invention has: partition walls 2 arranged in such a manner as toform a plurality of cells 3 extending from one end face 42 to the otherend face 44 through an axial direction; an outer peripheral wall 7 whichsurrounds an outer periphery of the partition wall 2; and pluggingportions 4 a, 4 b arranged in such a manner as to plug the cell 3 ineither end face.

An important characteristic of the present invention lies in that, asshown in FIG. 1(b), at least some of plugging portions 4 a arranged inthe vicinity of the outer peripheral wall 7 protrude from the end face42, and a tip 6 of a protruding portion 5 is substantially flat as shownin FIGS. 2(a) to (h), or has a moderate curved face as shown in FIGS.3(a) to (e).

By this configuration, as shown in FIG. 4, in a case where the pluggedhoneycomb structure is fixed by a fixing member 22, and stored in a canmember 20, the tip 6 is brought into contact with the fixing member 22,and the fixing member 22 is not brought into direct contact with theouter peripheral wall 7 or the partition wall 2 forming a cell 3 a inthe vicinity of an outer periphery. Although cracks are easily generatedby thermal expansion at a time when the fixing member moves toward anouter periphery, the cracks can be reduced in the outer peripheral wall7 and/or the partition wall 2 forming the cell 3 a in the vicinity ofthe outer periphery.

Moreover, since the cell 3 a in the vicinity of the outer periphery isnot directly covered with the fixing member 22, a fluid to be treatedcan flow into the cell in the vicinity of the outer periphery, andpressure losses can be reduced. Furthermore, a temperature differencecan be reduced between the cell in the vicinity of the outer peripheryand the inner cell, and a possibility of the crack by thermal stress canbe reduced.

From this viewpoint, the protruding portion according to the presentinvention needs to simply protrude, and further a tip needs to besubstantially flat or have a moderate curved face. As shown in FIG. 13,when the protruding portion 5 has a conical or pyramid shape as shown inFIG. 13, an excessive stress is applied to the tip at a time when thestructure is fixed by the fixing member, and this causes the cracks inthe protruding portion or the vicinity of the outer peripheral wall.Here, when the tip 6 is substantially flat, it is meant that the tip ofthe protruding portion has a substantially flat portion. The flatportion is preferably as flat as possible, and flatness is preferablyabout 0.05 mm or less. The flatness of 0.05 mm mentioned herein is thesame definition as that of a flatness prescribed by JIS-B0021, meansthat a contour of the face exists in a space having a width of 0.05 mm,and means that an actually measured flatness value of the flat facewhich is an object is 0.05 mm or less. For example, plugging portionsprotruding height from a filter end face is about 0.005 to 0.02 mm. Acase where the actually measured flatness value of the protrudingportion is 0.01 mm is included in a range of the flatness of 0.05 mm orless. An area of this flat portion may be usually small, but ispreferably 5% or more of a sectional area of one cell, that is, asectional area of plugging portions main body, more preferably 20% ormore from a viewpoint that the fixing member be smoothly moved. Thesmaller flatness of the flat portion is better, and the flatness ispreferably 0.05 mm or less. However, when the flatness is smaller, it isactually difficult to prepare the portion. The flatness may increase toabout 2 mm by the protruding height of the plugging portion tip and thearea of the flat portion, but is practically preferably about 0.1 orless, further 0.5 mm or less, when considering a preparing property, andpositional precision or stability of the fixing member. When adifference is excessively large between heights of the protrudingportions of the respective plugging portions, the stability of thefixing member is not satisfactory. Therefore, the flatness in the wholeprotruding portion is also important, and is practically 2 mm or less,preferably 1 mm or less. In short, the fixing member 22 is preventedfrom being brought into contact with the end portion of the partitionwall. Alternatively, even when the member is brought into contact, acontact face pressure is set to be little between the fixing member andthe partition wall end portion, and the fixing member may be smoothlymoved. When the tip 6 has a moderate curved face, the tip of theprotruding portion has a curved face portion to such an extent that thefixing member can smoothly move. Specifically, a curvature radius in theplugging tip portion is R 0.1 mm or more, preferably R 0.5 mm or more,further preferably R 1 mm or more.

When the protruding portion 5 has the above-described tip 6, there isnot any special restriction as to a configuration of the wholeprotruding portion, but a substantially flat tip is a preferableconfiguration. For example, as shown in FIGS. 2(a) to (h), there is anexample of a configuration in which a parallel sectional shape is asubstantially quadrangular shape such as a substantially rectangularshape and a substantially trapezoidal shape. Here, the substantiallyquadrangular shape includes a quadrangular shape whose corner portionhas been cut off in addition to a quadrangular shape. As shown in FIGS.5(a), (b), the quadrangular shape has a parallel sectional shape whosecorner portion has been cut into a linear or curved shape, and this ispreferable from a viewpoint of suppressing the cracks in the vicinity ofthe outer peripheral wall by smooth movement of the fixing member. Thatis, the tip preferably has a shape whose corner portion has beenchamfered. As a preferable specific example of the tip having a moderatecurved face, the tip has one domed shape as shown in FIGS. 3(a) to (d),and the tip has two or more domed shapes as shown in FIG. 3(e).

There is not any special restriction as to the orthogonal sectionalshape of the protruding portion. As a specific preferable configuration,the protruding portion preferably includes a portion having asubstantially circular sectional shape as shown in FIG. 6(a), or asubstantially polygonal sectional shape as shown in FIG. 6(b), andpreferably includes a portion having a sectional shape similar to thatof the cell. When the sectional shape of the cell is a substantiallypolygonal shape such as a substantially quadrangular shape, theprotruding portion preferably has a shape which starts from the sameshape as the sectional shape of the cell and which changes into apolygonal shape having more corner portions or a substantially circularshape toward the tip. Here, the substantially circular shape include anelliptic shape, a race track shape and the like in addition to thecircular shape, and the substantially polygonal shape includes a shapewhose corner portion has been cut into a linear or curved shape inaddition to a usual polygonal shape. Moreover, in a case where thesectional shape of the protruding portion includes a substantiallypolygonal portion, the substantially polygonal shape is preferable whosecorner portion has been cut into the linear or curved shape from aviewpoint of suppressing chipping of the corner portion.

In the protruding portion 5, there is not any special restriction as toa height from the end face 42 of a plugged honeycomb structure shown inFIG. 5(a), that is, a maximum height h of the protruding portion.However, when the maximum height h of the protruding portion isexcessively large, the protruding portion easily chips. When the heightis excessively small, a fluid to be treated does not easily flow intothe cell in the vicinity of the outer peripheral wall, and this is notpreferable. The maximum height h of the protruding portion is preferably20 μm or more, further preferably 0.2 mm or more, especially furtherpreferably 0.5 mm or more, preferably not more than a cell pitch length,further preferably 80% or less of the cell pitch length, furtherespecially preferably 50% or less. The maximum height of each protrudingportion may differ. However, the maximum height of the protrudingportion of each plugging portion disposed in at least the in thevicinity of the outer peripheral wall is substantially equal, and thisis preferable from a viewpoint that stress of the fixing member bescattered. From a viewpoint of ease of preparation, the maximum heightsof the protruding portions of all the plugging portions are preferablysubstantially equal. As to a combination with the flatness of the fixingmember, when the flatness of the fixing member is satisfactory, and theheight of the protruding portion is substantially equal, the height ofthe protruding portion is less than 20 μm. In this case, the flatness is0.02 mm, and the protruding portion is preferably 5 μm or more atminimum.

Porosity of the protruding portion of the plugging portion is set to besmaller than that of another portion of the plugged honeycomb structureto densify the structure. Accordingly, effects can be expected that theprotruding portion develops strength sufficiently bearing the contactwith the fixing member, and the surface of the protruding portion issmoothened to reduce friction with the fixing member. As means forreducing the porosity, there is a method in which a slurry component ofa plugging agent is adjusted beforehand, and the structure is fired insuch a manner that the porosity of the plugging portion is set to besmaller than that of a honeycomb structure main body. The protrudingportion may be coated with a component such as cordierite, silica, andalumina. A Ti-based or W-based hard material may be flame-sprayed to thesurface of the protruding portion. That is, the porosity of the wholeplugging portion is reduced, accordingly the porosity of the protrudingportion is set to be smaller than that of the partition wall, this is apreferable configuration, and it is also a preferable configuration toreduce the porosity of the only protruding portion in the pluggingportion.

In the present invention, at least some of the plugging portions whichplug the cells arranged in the vicinity of the outer peripheral wallneed to have the above-described protruding portions, and it is notessential that all the plugging portions for plugging the cells arrangedin the vicinity of the outer peripheral wall have the above-describedprotruding portions. However, from a viewpoint that the stress appliedto the protruding portion from the fixing member be scattered, all theplugging portions for plugging the cells arranged in the vicinity of theouter peripheral wall preferably have the above-described protrudingportions. From a viewpoint that the plugging portion be easily formed,all the plugging portions preferably have the above-described protrudingportions.

Here, the vicinity of the outer peripheral wall include the celladjacent to the outer peripheral wall, a range of the vicinity changeswith a width of the fixing member, and the range is preferably within 5mm from the outer peripheral wall, further preferably within 20 mm.Needless to say, even when some or all of the plugging portions arrangednot only in the in the vicinity of the outer peripheral portion but alsoin a portion other than the vicinity of the outer peripheral portionhave the protruding portions according to the present invention, thatis, even when the protruding portions exist over the whole region of theend face of the honeycomb structure, there is not any practical problem.In the practical use, various foreign matters, for example, oxidizedscales from an inner wall of an exhaust tube fly on a flow of an exhaustgas from an exhaust gas upstream of the honeycomb structure, that is,from an engine direction at a high speed, and collide with an exhaustgas inlet end face of the honeycomb structure. Therefore, there is apossibility that a thin partition wall of the honeycomb structurebreaks. In this case, when the protruding portion is disposed in theplugging portion in such a manner as to cover a partition wall tipportion as shown in FIGS. 2 (c), (f) or FIG. 3 (c), direct collision ofthe foreign matters can be prevented with respect to the partition wall.Therefore, the protruding portion of the plugging portion is preferablyformed over the whole region of the end face of the honeycomb structure.When the protruding portion is formed, a contact area with the exhaustgas increases, and therefore heat exchange is improved between theplugging portion and the exhaust gas. Since the plugging portion has alarger volume and a larger heat capacity as compared with a peripheralpartition wall portion, a follow-up property at exhaust gas temperatureis low, a temperature difference is large between the plugging portionand the partition wall portion, and thermal stress is easily generated.When the heat exchange is improved between the plugging portion and theexhaust gas, it can be expected that the temperature difference isreduced, and the thermal stress is suppressed. Therefore, the protrudingportion of the plugging portion is preferably formed over the wholeregion of the end face of the honeycomb structure. Therefore, theprotruding portions are preferably disposed in all the plugging portionsin the honeycomb structure end face, but this is not necessarilyrequired, and the protruding portions may be appropriately disposed inaccordance with a use environment at a practical use time. It is to benoted that the honeycomb structure of the present invention hasresistance to the above-described collision with the foreign matters,and an effect of reducing the thermal stress. Therefore, even in a usemode in which any fixing member is not used, for example, a canningstructure in which a can member is held without using any fixing member,the plugged honeycomb structure of the present invention can beeffectively used. The plugged honeycomb structure is sometimes placed ona face of a base or floor at a transfer time of the plugged honeycombstructure or a handling time. In this case, the corner portion (endportion of the outer peripheral wall) of the end face outer peripherychips in some case. In a case where the plugged honeycomb structure ofthe present invention is laid on the face of the base, floor or thelike, the corner portion of the end face outer periphery is not broughtinto direct contact with a lower surface, and there is an effect ofpreventing the chipping. When the protruding portions are formed on theplugging portions in opposite end faces of a DPF, either lower end facepreferably has the effect of preventing the chipping.

There is not any special restriction as to a shape or a material of theplugged honeycomb structure in the present invention, as long as thestructure has: for example, as shown in FIGS. 1(a), (b), partition walls2 arranged in such a manner as to form a plurality of cells 3 extendingfrom one end face 42 to the other end face 44 through an axialdirection; an outer peripheral wall 7 which surrounds the outerperiphery of the partition wall 2; and plugging portions 4 arranged insuch a manner as to plug the cells 3 in either end face 42, 44. Theorthogonal sectional shape of the plugged honeycomb structure can beappropriately determined, for example, from a circular shape, ellipticalshape, race track shape, quadrangular shape and the like in accordancewith application or installation place. The orthogonal sectional shapeof the cell may be a substantially polygonal shape such as a polygonalshape like a triangular shape, quadrangular shape, or hexagonal shape,or a substantially circular shape such as a circular shape and anelliptical shape. A cell density may be set to, for example, about 6 to2000 cells/square inch (0.9 to 311 cells/cm²), preferably 50 to 1000cells/square inch (7.8 to 155 cells/cm²). As shown in FIGS. 1(a), (b),the adjacent cells 3 have plugging portions 4 a, 4 b in mutuallyopposite end faces, and the plugging portions are arranged in such amanner that the respective end faces 42, 44 form a checkered pattern.There is not any special restriction as to materials of the pluggingportion, partition wall, and outer peripheral wall, but a ceramic or ametal is preferable, the ceramic is especially preferable from aviewpoint of heat resistance or the like. When the structure is used asa catalyst carrier or a filter, the partition wall and the outerperipheral wall is preferably porous. When the plugged honeycombstructure of the present invention is contained in a can member andused, an elastic member is preferably disposed such as a ceramic-formedmat between the can member and the outer peripheral wall.

Next, a manufacturing method will be described capable of preferablymanufacturing the plugged honeycomb structure of the present invention.This method includes a plugging step of plugging at least some of thecells 3 in either end face in a honeycomb structure 10 having thepartition walls 2 arranged in such a manner as to form a plurality ofcells 3 extending from one end face 42 to the other end face 44 throughthe axial direction as shown in FIGS. 7(a), (b). Moreover, the pluggingstep includes a masking sub-step, and a filling sub-step.

In the masking sub-step, as shown in FIG. 8, a film 12 is disposed inthe end face in such a manner as to mask some cells, that is, cells inwhich any plugging portion is not formed in the end face. In this step,the film 12 may be attached to the end face in a state in which a hole13 is made in a portion of the film 12, corresponding to thepredetermined cell in which the plugging portion is formed in the endface, that is, the portion of the film disposed on the predeterminedcell. After attaching the film 12 which does not have any hole to theend face in such a manner as to cover all the cells, the hole 13 is madein the predetermined cell in which the plugging portion is formed. Thisis preferable because the hole is correctly made in the targeted cell.

In a case where the hole 13 is made in the film 12 after disposing thefilm in this manner, the hole is made in such a manner that theperiphery of the hole 13 is raised in a thickness direction of the film,for example, as shown in FIG. 9(a), and this is preferable in that aplugging material can be applied in such a manner as to form aprotruding portion having a sufficient height in the filling sub-step.An example of a specific method of making the hole in this mannerincludes a method in which the film is heated in such a manner as to bemolten toward the outside from a center of the hole to make the hole.Further specifically, a predetermined position is preferably irradiatedwith laser light or the like to make the hole.

There is not any special restriction as to a type of the film. Forexample, a film which is molted by heating is preferable as a preferableexample, and a film which is holed by the laser light is furtherpreferable. The film preferably has an adhesive layer in such a mannerthat the film is sufficiently fixed after disposed on the end face.Specifically, the film has a substrate layer and the adhesive layer, thesubstrate layer is formed of a polymer material such as polyester,polyolefin, and halogenated polyolefin, and the adhesive layer ispreferably formed of an acryl-based adhesive material. The film has athickness of about 10 to 100 μm from viewpoints of strength and ease ofmaking the hole.

In the filling sub-step, the cell in which the hole has been made isfilled with a plugging material 14. In a conventional filling step, asshown in FIG. 14(a), the plugging material 14 formed into awater-containing slurry is poured into a slurry container 16, an endface 42 of a masked honeycomb structure 10 is immersed into the pluggingmaterial 14 formed into the slurry, and the predetermined cells arefilled with the plugging material 14. In this method, when the honeycombstructure 10 is taken out of the slurry container, a liquid in theslurry with which the cells are filled leaches in the porous partitionwall or the outer peripheral wall. As shown in FIG. 14(b), a tip 15 ofthe slurry moves toward the cell from the upper face of the film, andthe only plugging portion can be formed having a height equal to orlower than that of the end face of the honeycomb structure.

In the present invention, as shown in FIG. 10, a plugging material 14 ischarged up to a height which is not less than a height equal to that ofan upper face 17 of the film, and therefore the plugging portion havingthe protruding portion can be preferably formed. Here, the upper face ofthe film means a face of the film on a side opposite to the honeycombstructure. Thus, in a preferable method in which the cell is filled withthe plugging material up to the height not less than the height equal tothat of the upper face of the film, for example, first the pluggingmaterial is applied once, a tip 15 of the plugging material moves towardthe cell as shown in FIG. 14(b), and thereafter the plugging material isfurther applied. This is based on finding that after the tip of theplugging material moves by first filling, the tip of the pluggingmaterial hardly moves even when the plugging material is furtherapplied. Usually, the cell can be filled up to the height which is notless than that of the upper face of the film by two applications, butthe plugging material may be applied three or more times.

The slurry is poured beforehand in a container for the plugging, thefilm in which the holes have been made in a zigzag shape is attachedbeforehand to the honeycomb structure, the structure is fixed to amovable portion of a press with a chuck, the structure is pressed intothe container under a pressure of 0.01 to 5 MPa at a speed of 0.1 to 10mm/sec., and the slurry in the container is injected into the cell fromthe made holes. The honeycomb structure is chucked in such a manner thatthe honeycomb end face extends in parallel with the container. When thehoneycomb structure is pressed into the container, the honeycombstructure is sealed in such a manner as to prevent a plugging materialslurry from being leaked from an outer peripheral portion of thestructure. The sealing may be unnecessary in a case where a slurryamount is small in order to set a plugging depth to be small. Aftercompleting the press-in, the structure is removed from the container.When the honeycomb structure is slightly rotated, the structure can beeasily removed from the container.

Viscosity of the plugging material slurry is preferably in a range of 10to 1000 dPa·s. When the viscosity is in this range, the slurry is easilyheld in the cell in a case where the cell is filled with the slurry, anda predetermined plugging portion can be easily formed. Since the slurrydoes not become excessively hard, the cell can be easily filled with theslurry. The cell partition wall can be prevented from beingpushed/broken at a slurry filling time.

The viscosity of the slurry is further preferably in a range of 100 to600 dPa·s. When the viscosity is in this range, it is possible topreferably suppress a phenomenon in which the liquid in the slurrycharged into the cell leaches in the porous partition wall or the outerperipheral wall, kink of the plugging material is reduced, and thenumber of filling times can be reduced to enhance productivity. Eveneach corner of the cell is easily filled with the slurry, and a gap canbe easily prevented from being generated between a cell corner and theplugging portion.

When the gap is generated between the cell corner and the pluggingportion, a capturing performance of the filter degrades. However, when acapturing efficiency is in an allowable range, the gap may be sometimesgenerated between the cell corner and the plugging portion in order toreduce the pressure loss of the filter or to discharge an ash componentdeposited in the cell from the gap.

Accordingly, the viscosity of the plugging material slurry isintentionally increased in order to suppress rise of the pressure lossby long-term deposition of the ash component, and the gap is generated.

In another preferable method of filling the cell with the pluggingmaterial up to the height which is not less than that of the upper faceof the film, a liquid which does not substantially penetrate thepartition wall is used in a liquid component in the slurry pluggingmaterial, and accordingly the tip of the plugging material is preventedfrom being moved. By the use of this method, the cell can be filled withthe plugging material up to the upper face of the film by one filling.Here, when the liquid does not substantially penetrate, it is meant thatthe liquid only penetrates to such an extent that a length for movingthe tip of the plugging material toward the cell is about 50 μm or less,preferably 30 μm or less, further preferably 10 μm or less. This liquid,that is, a plugging agent slurry is a liquid having high viscosity, andspecifically a water content in the slurry is lowered as much aspossible, or a thickening agent can be added as an auxiliary agent tothe plugging agent slurry to adjust the viscosity.

Moreover, as still another preferable method, there is a method in whicha material having a water-absorbing or retaining property is added tothe plugging material slurry to reduce a drying speed of the slurry.Since the water-absorbing or retaining material holds the water content,it is possible to suppress a phenomenon in which the water content inthe slurry charged into the cell leaches in the porous partition wall orthe outer peripheral wall by addition of this material.

Moreover, since the rapid movement of the plugging material or the watercontent in the slurry is physically inhibited by the added material, aneffect of apparently raising the slurry viscosity is supposed to exertan influence, therefore the water-absorbing or retaining material ismore preferable, but the material does not necessarily have anywater-absorbing or retaining property.

The material preferably decomposes, flies/scatters, and disappears indrying or firing after the plugging/filling, but may not decompose,fly/scatter, or disappear as long as plugging portions characteristic isnot adversely influenced during or after the firing, or may react withthe plugging material.

Examples of the material which decomposes, flies/scatters, anddisappears include: powdered organic materials derived from plant, suchas flour, starch, and walnut shell; powdered synthetic resins such asPET, PMMA, phenol resin, polyethylene, and urethane; powdered carbonmaterials such as graphite, cokes, coal, activated charcoal, and tubularcarbon; hollowed synthetic resins such as foaming resin, non-foamedfoaming resin, and water-absorbing polymer; and solid liquid or gasmaterials at normal temperature, such as ice and dry ice. Examples ofthe material which does not decompose, fly/scatter, or disappear orwhich reacts with the plugging material include: high-melting materialssuch as alumina, mullite, aluminum titanate, zirconia, silicon nitride,silicon carbide, titania, tungsten carbide, and molybdenum; porousmaterials such as silica gel and zeolite; and hollow inorganic materialssuch as fly ash balloon, silastic balloon, and silica beads. Thehigh-melting material mentioned here is a material having a meltingpoint which is higher than a firing temperature of a plugging materialmain component. For example, when the plugging material main componentis cordierite, nonoxide-based materials are preferable such as siliconnitride and silicon carbide as the high-melting materials because thematerials are stable in the firing of cordierite in an oxide atmosphereat about 1400° C.

A shape of the material may be not only particulate but also fibrous,and the powder means that both the particulate and fibrous materials arecontained. The material is preferably hollow rather than solid intreatment of a generated gas at a decomposition, flying/scattering, anddisappearing time. These materials may be used alone or compounded.Added amounts of these materials are appropriately determined based onsettings of viscosity of the plugging slurry and plugging materialporosity after the firing, and therefore are not especially restricted.

Among the materials, the hollow synthetic resins like the foaming resin,non-foamed foaming resin, and water-absorbing polymer, and porousmaterials such as silica gel have water-absorbing properties, and arepreferable for the above-described reason. After filling the cell withthe plugging material, a material is added which causes volume expansionby thermal treatment or the like. Accordingly, the plugging material inthe cell causes the volume expansion, the plugging portion protrudesfrom the filter end face, and the protruding portion can be easilyformed. For example, when the non-foamed foaming resin is added to theplugging material beforehand, and the cell is filled with the pluggingmaterial and thermally treated at 100 to 250° C., the non-foamed resinfoams, and the volume of the plugging portion expands. Furthermore, forexample, when the water-absorbing synthetic resin or urethane is addedto the plugging material beforehand, the cell is filled with theplugging material, and thereafter the water content is added to theplugging material, the volume of the water-absorbing synthetic resin orurethane is expanded to expand the volume of the plugging portion.Additionally, when bubbles are intentionally generated in the pluggingmaterial slurry, and the cell is filled with the slurry in such a mannerthat the bubbles remain in the plugging portions, the porosity of theplugging portion can be raised.

Moreover, when various materials are added, the porosity of the pluggingportion increases, the thermal capacity of the plugging portion islowered, and burning of particulate matters (PM) in the filter ispromoted. Furthermore, even in a case where a catalyst is carried in thefilter, the PM is oxidized/burnt utilizing activity of the catalyst, andtoxic components in the exhaust gas are treated, there is an effect thatthe thermal capacity of the plugging portion is lowered to therebyenhance the catalyst activity. On the other hand, in a conventionaltechnique, filter temperature does not easily rise especially in thecell in the vicinity of the plugging portion because of high thermalcapacity of the plugging portion, and the catalyst activity drops.Furthermore, when the porosity of the plugging portion is increased, orsince the plugging portion has a difference in rigidity from a regionbetween the plugging portions on opposite ends of the filter, therigidity of the plugging portion is lowered, accordingly the rigiditydifference is reduced, and the resistance to thermal shock of the filteris enhanced. Stress concentration in the vicinity of the pluggingportion can be relaxed in a case where the filter outer peripheralsurface is grasped by a mat or the like. When the porosity of theplugging portion is raised, sufficient permeability is imparted to theplugging portion, the exhaust gas can pass through the plugging portion,and there is an effect of reducing the pressure loss of the filter.Furthermore, when the rigidity of the honeycomb substrate is broughtclose to that of the plugging portion in a stage of manufacturing thefilter, cracks can be reduced in the vicinity of the plugging portion ata firing time.

Moreover, when the cell is filled with the plugging material in thismethod, in the masking sub-step, as shown in FIG. 9(a), the holes aremade in such a manner that the peripheries of the holes 13 are raised inthe film thickness direction, accordingly, as shown in FIG. 9(b), thecells can be filled with the plugging materials 14 up to positionshigher than the upper face 17 of the film, and the protruding portionscan be formed whose tips are disposed in positions higher than the upperface of the film. Even when the liquid leaches in the partition wall orthe like, and the tip of the plugging material moves toward the cell, itis possible to hold the tip of the plugging material at the height whichis not less than that of the upper face of the film.

After the filling sub-step, the plugging portions having the protrudingportions can be formed usually by drying, heating, and/or firing. It isto be noted that, in general, the honeycomb structure can bemanufactured by firing after forming as described later, but theplugging step may be performed with respect to a formed article havingthe honeycomb structure before the firing, or may be performed withrespect to a fired article having the honeycomb structure after thefiring.

In the honeycomb structure according to the present invention, forexample, a raw material is a powder of at least one type of materialselected from a group consisting of: various ceramics such ascordierite, mullite, alumina, spinel, zirconia, silicon carbide, siliconcarbide-cordierite-based composite material, silicon-siliconcarbide-based composite material, silicon nitride, lithium aluminumsilicate, aluminum titanate, and zeolite; metals such as anFe—Cr—Al-based metal; and a combination of them. To this raw material,binders are added such as methyl cellulose and hydroxypropoxyl methylcellulose. Furthermore, surfactant and water are added to form a plasticpuddle, and the puddle is extruded into a honeycomb shape.Alternatively, after forming the honeycomb shape, the honeycombstructure can be prepared by the firing. Various ceramics and metals arepreferable as main components of the plugging material, at least onetype is further preferably selected from the group of the preferable rawmaterials of the honeycomb structure, and the raw material is especiallypreferably common to that of the honeycomb structure to be plugged.Moreover, this main component is a main component of the pluggingportion.

EXAMPLE AND COMPARATIVE EXAMPLE

A manufacturing method of the present invention will be describedhereinafter further specifically based on one specific example. First,as a raw material blending and kneading step, a foaming resin is addedas a pore former to silica, kaolin, talc, and alumina which arecordierite materials, further a binder, dispersant, and water are added,the materials are kneaded into a clay form. The pore former may havesuch a property that the former flies/scatters/disappears by a firingstep. Inorganic materials such as a carbon material, a polymer compoundsuch as a plastic material, and an organic material such as starch maybe used alone or in combination. Next, as a forming and drying step, thekneaded clay-like material is used, and extruded to form a honeycombstructure, and the structure is dried. As drying means, various methodscan be performed, but the drying is preferably performed in a method ofcombination of microwave drying and hot-air drying, or induction dryingand hot-air drying. Additionally, a special method such asfreezing/drying is applicable. Next, opposite end faces of the driedhoneycomb structure is cut into predetermined lengths.

Next, the process shifts to a plugging step. First, in a maskingsub-step, a film is disposed on the end face. As a film material, apolyester film (maker: Teraoka Seisakusho, model number: 631S#25, filmthickness: 50 μm) is used. One face of the film is coated with anadhesive, and the film is attached to the end face of the honeycombstructure. Next, cell openings are made into zigzag shapes in thehoneycomb structure end face to which the polyester film has beenattached by an NC scannable laser apparatus. When the holes are made,the film melts, and peripheries of the holes are raised by influence ofthe melting.

Next, the process shifts to a filling sub-step. Water, binder, andglycerin are added to the cordierite material to form a slurry of about200 dPa·s, the slurry is poured in a plugging container beforehand, andthe honeycomb structure is fixed to a movable portion of a press machinewith a chuck. The film has been attached to the honeycomb structure, inwhich the holes have been made in the zigzag shapes. The structure ispressed into the container at a pressure of 0.25 MPa at a speed of 1mm/sec, and the slurry in the container is injected into the cells fromthe made holes. The honeycomb structure is pressed into the container insuch a manner that end face of the honeycomb structure extends inparallel with the container. When the honeycomb structure is pressedinto the container, the honeycomb structure is sealed in such a manneras to prevent a plugging material slurry from being leaked from an outerperipheral portion of the structure. After completing the press-in, thestructure is removed from the container. When the honeycomb structure isslightly rotated, the structure can be easily removed from thecontainer. The plugging portions for plugging the cells are formed inthe end faces of the honeycomb structure in this manner. Since a watercontent in the injected slurry is absorbed by the honeycomb structure,the plugging material kinks, and a tip of the plugging portion is insidea film upper-face position (rising upper-face position around the hole).Here, the plugging material slurry is inserted into the made holes. Whenthe water content of the plugging material slurry is adjusted to therebyincrease slurry viscosity to 450 dPa·s, the kink of the pluggingmaterial can be suppressed. Furthermore, even when 5% of a foaming resinis added, the kink of the plugging material can be reduced.

Next, to dry a plugging agent, hot air at 140° C. is applied to theplugged end face of the honeycomb structure to dry the structure forabout five minutes without peeling the film. The drying is possible evenwith a hot plate. When the film is peeled after the drying, the tipportion of the plugging is plugged into a convex shape. This issimilarly performed with respect to another end face, and accordinglyprotruding portions can be formed on the plugging portions on oppositeend faces. Thereafter, when the firing is performed, a cordieriteplugged honeycomb structure is obtained.

When porosity was measured by a mercury porosimeter with respect to apartition wall of the cordierite plugged honeycomb structure actuallyobtained based on the above-described method, the porosity was 67%, andan average pore diameter was 27 μm. The cell had a quadrangular shapehaving a partition wall thickness of about 0.3 mm, and a cell pitch ofabout 1.6 mm, and filter dimensions were a diameter of about 191 mm, anda length of about 200 mm. A plugging length from a filter end face to acell passage inner direction was set to about 3 mm, and a height of theprotruding portion was set to 0.2 to 0.4 mm (flatness in the wholeprotruding portion: 0.2 mm).

The plugged honeycomb structure having the protruding portions weremanufactured in this manner based on the present invention,pressed/grasped as a DPF into a metal case (can member) with a ceramicmat (trade name: Interam Mat, manufactured by 3M Co., Ltd.), thereafteropposite end faces of the DPF were fixed with fixing members, the fixingmembers were welded to the metal case, and the metal case was connectedto a cone to manufacture a converter assembly. A converter assembly wasalso manufactured using a conventional plugging structure DPF withoutany protruding portion. The manufactured converter assembly wasconnected to an exhaust system of an actual diesel engine (displacement:about 5 liters), an exhaust gas was passed to perform a heating/coolingtest, and the converter assembly was disassembled to check the DPF.Then, cracks were generated in a DPF end face outer peripheral portionin the converter assembly having a conventional structure, but any crackwas not generated in a DPF end face outer periphery in the converterassembly by the present invention.

INDUSTRIAL APPLICABILITY

As described above, a plugged honeycomb structure of the presentinvention does not easily break, and is capable of enhancing durabilityso that the structure is preferably usable in a filter such as a DPF. Bya method of manufacturing a plugged honeycomb structure of the presentinvention, this plugged honeycomb structure can be preferably prepared.

1-18. (canceled)
 19. A plugged honeycomb structure comprising: partitionwalls arranged in such a manner as to form a plurality of cellsextending from one end face to the other end face through an axialdirection; an outer peripheral wall which surrounds an outer peripheryof the partition wall; and plugging portions disposed in such a manneras to plug the cell in either end face, characterized in that at leastsome of the plugging portions arranged in at least the vicinity of theouter peripheral wall protrude from the end face, and a tip of aprotruding portion is substantially flat or has a moderate curved face.20. The plugged honeycomb structure according to claim 19, wherein someor all of the plugging portions arranged in a portion other than thevicinity of the outer periphery protrude from the end face, and the tipof the protruding portion is substantially flat or has the moderatecurved face.
 21. The plugged honeycomb structure according to claim 19,comprising a plugging portion including a protruding portion including aportion whose sectional shape crossing the axial direction at rightangles is substantially circular.
 22. The plugged honeycomb structureaccording to claim 19, comprising a plugging portion including aprotruding portion including a portion whose sectional shape crossingthe axial direction at right angles is a substantially polygonal shape.23. The plugged honeycomb structure according to claim 22, wherein thesubstantially polygonal shape has a shape whose corner portion has beencut into a linear or curved shape.
 24. The plugged honeycomb structureaccording to claim 19, comprising a plugging portion including aprotruding portion whose sectional shape parallel to the axial directionis a substantially quadrangular shape.
 25. The plugged honeycombstructure according to claim 24, wherein the substantially quadrangularshape is a shape whose corner portion has been cut into a linear orcurved shape.
 26. The plugged honeycomb structure according to claim 19,wherein a maximum height from the end face to the tip of each protrudingportion is substantially equal.
 27. The plugged honeycomb structureaccording to claim 19, wherein porosity of the protruding portion issmaller than that of another portion of the plugged honeycomb structure.28. A method of manufacturing a plugged honeycomb structure comprising:preparing a honeycomb structure comprising porous partition wallsarranged in such a manner as to form a plurality of cells extending fromone end face to the other end face through an axial direction, and aplugging step of plugging at least some of the cells in either end face,characterized in that the plugging step includes: a masking sub-step ofdisposing a film on the end face in such a manner as to mask some of thecells; and a filling sub-step of filling a predetermined cell which isnot masked with a plugging material, and the filling sub-step includes:filling the cell with the plugging material up to a height which is notless than a height equal to that of an upper face of the film.
 29. Themethod of manufacturing the plugged honeycomb structure according toclaim 28, wherein in the filling sub-step, the plugging material isapplied at least twice.
 30. The method of manufacturing the pluggedhoneycomb structure according to claim 28, wherein in the fillingsub-step, the plugging material is applied once.
 31. The method ofmanufacturing the plugged honeycomb structure according to claim 30,wherein the plugging material is a slurry including a liquid, and theliquid is a liquid which does not substantially penetrate into thepartition walls.
 32. The method of manufacturing the plugged honeycombstructure according to claim 28, wherein in the masking sub-step, thefilm is disposed in such a manner as to cover all the cells, and a holeis made in a portion of the film, corresponding to a predetermined cell.33. The method of manufacturing the plugged honeycomb structureaccording to claim 32, wherein a hole is made in such a manner thatperiphery of the hole is raised in a thickness direction of the film.34. The method of manufacturing the plugged honeycomb structureaccording to claim 28, wherein the plugging material is a slurrycontaining a liquid, and viscosity of the slurry is in a range of 10 to1000 dPa·s.
 35. The method of manufacturing the plugged honeycombstructure according to claim 28, wherein the plugging material is aslurry containing at least one type selected from a group consisting ofa powdered organic material derived from plant, powdered syntheticresin, powdered carbon-based material, hollow synthetic resin, solidnormal-temperature liquid or gas material, high-melting material, porousmaterial, and hollow inorganic material.
 36. The method of manufacturingthe plugged honeycomb structure according to claim 28, wherein afterfilling the cell with the plugging material, volume of the pluggingmaterial is expanded, and the protruding portion is protruded from thefilter end face.